fix: build vant-css failed

packages/vant-css/src/deep-select.css

@@ -1,10 +1,12 @@
-@import "./mixins/ellipsis";
-@import "./mixins/clearfix";
+@import "./mixins/ellipsis.css";
+@import "./mixins/clearfix.css";
 @import './common/var.css';
+
 .van-deep-select {
   user-select: none;
   position: relative;
   @mixin clearfix;
+
   &__nav {
     width: 143px;
     /*float: left;*/
@@ -16,31 +18,37 @@
     background-color: $c-white;
     -webkit-overflow-scrolling: touch;
   }
+
   &__nitem {
     line-height: 44px;
     padding: 0 15px;
     background-color: $c-white;
     @mixin multi-ellipsis 1;
+
     &--active {
       background-color: $c-background;
     }
   }
+
   &__content {
     padding: 0 15px;
     margin-left: 143px;
     overflow: scroll;
     -webkit-overflow-scrolling: touch;
   }
+  
   &__item {
     position: relative;
     line-height: 44px;
     padding-left: 5px;
     padding-right: 18px;
     @mixin multi-ellipsis 1;
+    
     &--active {
       color: $button-danger-background-color;
     }
   }
+
   &__selected {
     float: right;
     position: absolute;

packages/vant-css/src/goods-action.css

@@ -1,4 +1,5 @@
 @import './common/var.css';
+@import './mixins/border_retina.css';
 
 .van-goods-action {
   left: 0;